The Launcher Barrel can be found in the north-west corner in Loading Bay 2, considering you're looking at the map. Here you will find three boxes in front of a vent near a couple of containers. Use two boxes to make it possible for you to jump up the container, then grab the other box and jump up the container. Put down the box on the container and then while standing on the container grab one of the boxes you used to get on top of the container. Now use the two boxes on the container to make it possible for you to jump in the open container. Jump in and you will find the Launcher Barrel.

The Trigger Module can be found in the south-east corner in Loading Bay 1, inside a red container on top of a box. You might need to enter a blue container first and then remove a box, so you can go inside the red container.

After leaving Loading Bay 1 through the red door with turret above head right, then head left, and go right once more. Behind the first door on your left you will find the Scope Assembly. Either hack the keypad directly, level 2 hacking, or pick up the cardboard box next to the door and enter the opposite room. Place the box in front of the vent in this room and jump on top of the box and inside the vent. Follow the vent and you'll end up in the room with the Scope Assembly.

After collecting the three parts return to Quinn, he will give you the rocket launcher and it is quite beast :P.

The Trigger Module can be found in the south-east corner in Loading Bay 1, inside a red container on top of a box. You might need to enter a blue container first and then remove a box, so you can go inside the red container.